1. Field of the Invention
This invention pertains generally to roadway repair, and more particularly to an apparatus for applying hot sealants to cracks or similar areas to be filled upon a surface, such as a paved roadway surface.
2. Description of the Background Art
It will be appreciated that an unfilled crack in a paved roadway is subject to expansion from various sources, such as from ice formation, and that cracked surfaces can be subject to erosion. By filling cracks and similar voids in pavement surfaces, the longevity of the surface can be greatly increased. Typically these cracks, and similar small voids, are filled during pavement maintenance operations by melting a polymeric sealer and introducing a sufficient quantity of the sealer into the crack to completely fill it and seal it from the environment.
Hot sealants are often applied using a portable sealant melter that melts blocks of solid sealant material into a liquid state. The molten sealant is then retained in a sealant reservoir generally having a capacity of from about two hundred to about four hundred gallons, and is typically held at a temperature of over 300° F. for application. The sealant material is usually purchased in solid blocks that weight approximately twenty to fifty pounds.
Currently, the process of sealing cracks, such as in pavement, is subject to a number of drawbacks and inefficiencies that slow the work and increase the associated cost. In typical sealing applications, the sealant is dispensed from the sealant melter, into which blocks of solid sealant must be periodically added to maintain the reservoir of molten sealant at a desired level. Newly added blocks of sealant liquefy slowly, thereby constraining the rate at which the liquid sealant may be dispensed from the sealant melter system at the desired temperature. Due to the slow speed with which sealants are often applied manually, the slow rate of liquefaction generally does not pose a significant detractor of current sealant melting operations.
However, as sealant application becomes increasingly subject to automation, the slow rate at which solid blocks of sealant are liquefied can limit the speed of sealant application and associated operations.
One known approach to increasing the rate by which solid blocks are liquefied within a sealant melter is to route a series of large pipes, approximately two to three inches in diameter, over the heated sealant chamber opening and pass a heated oil through the pipes. The blocks of solid sealant material are placed over the pipes and required to melt under gravity feed in response to the heat in the pipes before entering the melting chamber. A number of minutes may pass before the block is melted and pieces of the block fall into the melter reservoir. Furthermore, the large pipe diameter, which is necessitated to provide sufficient rigidity, slows the transition of the material into the sealant reservoir, as a substantial portion of the block must be melted away prior to entry into the sealant reservoir. As a result, such “automated” systems are limited in their ability to rapidly melt sealant to a desired benchmark that the sealant blocks be divided within less than a minute to speed melting within the sealant chamber.
Additional drawbacks exist with regard to equipment used to dispense melted sealants. Typically, the heated sealants are dispensed from a heated chamber to an applicator head which then directs the liquid sealant into the pavement crack. Prior to reaching the applicator head, the heated sealant passes through a hose to reach the applicator. However, as the sealant flows through conventional hoses, heat is lost. As a result, sealant viscosity increases which can prevent proper application of the material, and in some cases lead to clogging within the hose. Furthermore, as a consequence of using an unheated hose, the viscosity of the liquid sealant during application is variable and depends on the rate at which the material is being applied, with longer delays during application leading to further cooling of the heated sealant in the hose. It should also be readily appreciated that stopping fluid flow through the hose for an extended period of time, such as thirty minutes, can allow the sealant to solidify in the hose and applicator head, requiring expensive servicing of the equipment.
Insulated and/or heated hoses have been created to remedy the situation and maintain a high liquid sealant temperature as it traverses the hose. These heated hoses generally rely on passing a heated fluid, such as an oil, through passageways within hoses joined to the exterior of the liquid sealant conveyance hose. This method of externally heating the sealant carrying hose so as to heat the contents therein has a number of drawbacks. First, the hose itself is subjected to temperatures from the heater that are substantially in excess of the desired sealant temperature in order to achieve a desired temperature within the faster flowing central portion of the hose passageway. It should be noted that the heat from the heated fluid is insulated from the sealant material being heated by the walls of the heated fluid hose and the walls of the sealant hose. Additionally, the common use of hoses with a circular cross section limits the heat conductive interface available between the heater hose(s) and the sealant hose. However, the incorporation of non-circular hoses leads to increased fabrication and maintenance costs. Secondly, the heating element must encircle the exterior of the hose to provide even heating of the flowing material. Thirdly, layers of insulation must be built up surrounding the combination of heating hose(s) and sealant hose to reduce the burn hazard posed to operators and to reduce heat losses. In view of the preceding discussion, it is not surprising that the resultant sealant hose has limited flexibility, is burdensome to maintain, and is prone to cracking along with similar leakage inducing conditions. Therefore, although current heated hoses provide a number of benefits they are also expensive, heavy, inflexible, prone to leakage, and are a burden to maintain.
Additional problems arise further downstream of the sealant hose during the application of sealants to cracks in pavement surfaces. Traditional sealant applicator heads, which receive liquid sealants through the sealant hose, rely on dispensing a flow of sealant over a crack to fill the crack under the effect of gravity and therein seal the crack. That approach, however, is subject to a number of detractors that limit application speed along with the benefits and longevity of sealing the crack. It should be recognized that cracks generally do not follow regular straight paths and that they vary in width and depth along the span of a given crack. Since the volume of the crack ultimately depends on crack width and depth, the amount of sealant required to fill the crack varies along the crack span. When manually applying sealants, the varying crack volume is accommodated by adjusting the speed of application or the rate at which sealant is dispensed so that an appropriate amount of sealant is applied. However, modulating sealant application speed is inefficient and not always practical. This is particularly true regarding systems which automatically dispense the heated sealant, in that the crack must be monitored as it is being filled while applicator motion must vary in response to crack capacity. Another approach is to match the sealant dispensing dynamics, such as flow rate, to the characteristics of the crack. However, this is difficult to achieve and, due to the delays involved, can lead to underflow or overflow of the sealant which can be considered a miss-fill of the crack. In addition, with either of these approaches, the sealant is only “drizzled” into the crack. As a result, the sealant generally does not seat deeply into the crack, thereby allowing water to enter the crack and further reduce the security of sealant retention while substantially reducing the effectiveness of the sealant patch.
Therefore, a need exists for advanced sealant delivery methods and devices that provide more efficient sealant delivery for filling of pavement cracks. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed pavement crack sealing devices and methods.